It has been well known that after a silver halide photographic light-sensitive material is exposed to light, an oxidized aromatic primary amine developing agent reacts with a dye forming coupler to form color images. In this process, color reproduction by a conventional substractive process is used to from color images composed of cyan, magenta, and yellow dyes, which are the complementary colors of red, green, and blue, respectively. The reaction of the coupler with the oxidation product of the color developing agent is carried out at an active site. The coupler having a hydrogen atom as a substituent at the active site is a 4-equivalent coupler, i.e., a coupler which stoichiometrically requires 4 mols of silver halide having a development nucleus as an oxidizing agent for forming 1 mol of dye.
On the other hand, a coupler having a group releasable in the state of an anion as substituent at the active site is a 2-equivalent coupler, i.e., a coupler which requires only 2 mols of silver halide having a development nucleus for forming 1 mol of dye. Accordingly, the processing time for the photographic light-sensitive materials can be shortened, and the sharpness of the color images formed is improved when the 2-equivalent coupler is used, as compared with using the 4-equivalent coupler, because it is generally possible to reduce the amount of silver halide in the light-sensitive layer and to reduce the thickness of the layer. Further, in 2-equivalent couplers, it is possible to change the coupling activity with respect to the color developing agent by changing the properties of releasing group.
Several attempts have been made to prepare 2-equivalent couplers from 5-pyrazoline type couplers which have been dominantly employed. For instance, the 4-position of the pyrazolone ring can be substituted with a thiocyano group as described in U.S. Pat. Nos. 3,214,437 and 3,253,924, an aryloxy group as described in U.S. Pat. No. 3,419,391, a 2-triazolyl group as described in U.S. Pat. No. 3,617,291, a halogen atom as described in U.S. Pat. No. 3,522,052, or an alkylthio group, an arylthio group or a heterocyclic thio group as described in U.S. Pat. No. 3,227,554, etc.
However, these 4-position substituted pyrazolone couplers have several diadvantages. They cause the formation of severe color fog; they have only a low coupling activity; they are chemically unstable per se and change into compounds which are unable to form color with the lapse of time; and they have many difficulties in their synthesis, etc.
Further, several 5-pyrazolone type two-equivalent magenta couplers having a heterocyclic substituent at the 4-position thereof are also known. More specifically, 5-pyrazolone couplers having at the 4-position thereof an imidazolyl group or a derivative thereof, a 1,2,4-triazolyl group or a derivative thereof or a 1,2,3-triazolyl group or a derivative thereof as described in West German Pat. (OLS) Nos. 2,536,191 and 2,651,353, or a pyrazolyl group or a derivative thereof as described in U.S. Pat. Nos. 4,310,619, 4,301,235 and 4,367,282, etc. are known.
Certainly, these couplers have good stability and color forming properties. However, they are still insufficient since increase in color image density may occur upon a lapse of time after processing of the photographic material containing them or they interact with a silver halide emulsion (for example, they adsorb to silver halide grains) whereby sensitivity is decreased.
Other compounds have been proposed as color formation improving agents or solubility improving agents, etc. More specifically, improvements in color formation and graininess provided by a carboxylic acid type compound having an ester group are described in European Pat. (OPI) No. 71, 122 (the term "OPI" as used herein means an "unexamined published application"). Further, in U.S. Pat. No. 3,700,454, it is described that an alkyl-substituted phenoxyalkyl carboxylic acid is employed as a solvent component for a coupler having an alkyl-substituted phenoxyalkanamido group to improve color forming property and solubility.
Silver halide color photographic materials (hereinafter simply referred to as color light-sensitive materials) are generally processed after color development by steps such as bleaching and fixing or bleaching, fixing and, further, washing with water, stabilizing, drying, etc. It has been strongly desired in recent years to conduct such processing in a shorter period of time. Such a requirement has been increased, particularly, for the processing of color light-sensitive materials for photographing, which usually require a processing time of 20 min. or longer.
In films such as color negative films or color reversal films which are printed or in which dye images formed are viewed using transmitted light, it is required that the dye images be formed in sufficient density and thus it is necessary to coat a great amount of silver halide in order to obtain high sensitivity. Further, it is also necessary to form a great amount of developed silver in a color developing step.
Coating of silver halide in such a great amount and formation of the developed silver in a great amount results in requiring a long period of time not only in the color developing step but also in a silver removing step including bleaching and fixing.
To reduce such a drawback, it has been known to use a two-equivalent coupler, requiring only two moles of silver halide having a development center instead of four-equivalent coupler, requiring four moles of silver halide having a development center stoichiometrically required for forming one mol of dye.
By the use of two-equivalent couplers, since the amount of silver halide in a light-sensitive layer can be reduced and the thickness of the layer can be reduced, significant benefits of rapid processing and improvement in the sharpness of the dye imagem can be obtained.
For this purpose, various two-equivalent cyan and yellow couplers have been practically used since they have high color forming properties and are stable themselves. However, magenta couplers have scarcely been put to practical use since their stability is inferior or their color forming performance is poor. For instance, 5-pyrazolone type couplers mainly used as magenta coupler with two-equivalent function, include pyrazolone ring substituted at the 4-position with thiocyano group described in U.S. Pat. Nos. 3,214,437 and 3,253,924, with aryloxy group described in U.S. Pat. No. 3,419,391, with 2-triazolyl group described in U.S. Pat. No. 3,617,291, with a halogen atom described in U.S. Pat. No. 3,522,052, with an alkylthio group, an arylthio group or a heterocyclic thio group described in U.S. Pat. No. 3,227,554, respectively.
However, when using the 4-position substituted pyrazolone couplers, there are several drawbacks: severe color fog is caused; coupling activity is much too low; the coupler is chemically unstable and turns into a compound incapable of color formation with the lapse of time; and there are many difficulties in view of their syntheses.
Further, 5-pyrazolone two-equivalent magenta couplers having a heterocyclic subtituent at the 4-position have been described in many patents. There have been proposed those couplers in which a 5-pyrazolone is substituted at the 4-position thereof with an imidazolyl group or its derivative, 1,2,4-triazolyl group or its derivative or 1,2,3-triazolyl group or its derivative as described in West German Pat. (OLS) Nos. 2,536,191 and 2,651,363; or with a pyrazole group or its derivative as described in U.S. Pat. Nos. 4,310,619, 4,301,235 and 4,367,282, etc.
Certainly, these couplers are stable themselves and have high coupling activity.
However, as described in Japanese Patent Application (OPI) No. 956/87, many of the above-described two-equivalent magenta couplers have various drawbacks in that they cause severe color fog; they have low coupling activity and cause insufficient color formation and the density of the dye image formed increases during preservation after processing, although the color forming properties thereof are good, etc.
Since such drawbacks of two-equivalent magenta couplers appear more remarkably in time-shortened processing, they can not actually attain the foregoing requirements, although they have a potential capability of reducing processing time.
Moreover, the reduction of processing time described above also permits miniaturization of a developing machine, and thus a large benefit is generally provided to color laboratories having a small working space. Therefore, in addition to the reduction of time for the color development step and the silver removing step including bleaching and fixing, it is desireble to shorten drying time, which requires the longest period in a conventional large size developing machine. For this purpose, various means have been investigated including, for example, increasing the amount of air for drying.
However, it has been found that when the color light-sensitive materials containing the above-describd azole releasing two-equivalent magenta couplers are processed using a drying step for 8 minutes or less, the density of the magenta color image gradually increases after processing. Due to this problem, it is not possible to reduce the drying step time when using the above-described two-equivalent magenta couplers, although color images having excellent sharpness are obtained. Consequently, it is difficult to sufficiently achieve the reduction in processing time which has been highly in the art.
In recent years, several approaches have been suggested for the purpose of reducing the amount of water used such as an amount of washing water, etc. in processing steps in view of environmental conservation, water resources or cost. For example, in S. R. Goldwasser "Water Flow Rates in Immersion-Washing of Motion Picture Film", Journal of the Society of Motion Picture and Television Engineers, No. 64, pages 248 to 253 (May, 1955), a method for reducing the amount of washing water by utilizing multi-stage water washing tanks and countercurrent water is proposed. Further, a system for saving water wherein color photographic materials are subjected to a stabilizing step substantially without a water washing step after a bleach-fixing step is disclosed in U.S. Pat. No. 4,336,324. These methods are effective for saving water, and have been applied to various types of automatic processing machines.
However, reduction of the amount of washing water leads to an increase in the amount of various kinds of processing solution components remaining in color light-sensitive materials after processing. The increase in the amount remaining causes fading of dye images or increases color stain after processing. These problems are particulrly notable when the processing time for a water washing step is reduced.
In order to solve these problems, the application of a multi-stage countercurrent process using a large number of tanks is disclosed in the article by S. R. Goldwasser mentioned above. However, the number of tanks for water washing is actually limited to 2 to 6 from the standpoint of the area required and cost. Therefore, this method is in sufficient. Another method is described in Japense Patent Application No. 233997/85 wherein fading is prevented by adding a sodium salt or potassium salt of a chelating agent to water for a washing step. However, this method has almost no effect on the fading of magenta dyes, although it is very effective in the prevention of fading of cyan dyes and yellow dyes. Further, it is described in Japanese Patent Application (OPI) No. 43741/86 that fading of magenta dyes is prevented by using a stabilizing solution with a controlled surface tension. However, it is difficult to obtain the desired effect.
Accordingly, in order to conduct development processing using a further reduced amount of water, development of a novel method which can prevent from degradation of image preservability, such as fading of magenta dyes and increase in color stain, has been strongly desired. In particular, it is important to solve the above-described problems in development processing of color photographic light-sensitive materials using two-equivalent magenta couplers, since two-equivalent magenta couplers have been mainly employed as magenta dye forming couplers in view of improvement in sharpness of images.